provide go doc comments for exported types and functions

pkg/store/disk.go

@@ -11,6 +11,7 @@ import (
 
 type disk string
 
+// Disk returns a local disk cache that stores files within a given directory.
 func Disk(dir string) Store { return disk(dir) }
 
 func (d disk) Put(ctx context.Context, snapshot Snapshot) error {

pkg/store/mem.go

@@ -13,6 +13,7 @@ type memory struct {
 	cache []Snapshot
 }
 
+// Memory creates an in-memory cache.
 func Memory() Store { return &memory{} }
 
 func (m *memory) Put(ctx context.Context, snapshot Snapshot) error {

pkg/store/store.go

@@ -7,12 +7,15 @@ import (
 	"github.com/sixt/gomodproxy/pkg/vcs"
 )
 
+// Store is an interface for a typical cache. It allows to put a snapshot and
+// to get snapshot of the specific version.
 type Store interface {
 	Put(ctx context.Context, snapshot Snapshot) error
 	Get(ctx context.Context, module string, version vcs.Version) (Snapshot, error)
 	Close() error
 }
 
+// Snapshot is a module source code of the speciic version.
 type Snapshot struct {
 	Module    string
 	Version   vcs.Version
@@ -20,6 +23,7 @@ type Snapshot struct {
 	Data      []byte
 }
 
+// Key returns a snapshot key string that can be used in cache stores.
 func (s Snapshot) Key() string {
 	return s.Module + "@" + string(s.Version)
 }